On underwater structures and on ship's hulls which are exposed to sea and/or fresh water, attachment and growth of marine organisms such as green algae, such as Enteromorpha spp. and Ulva spp., diatoms, such as Amphora spp., tubeworms, barnacles such as Balanus spp., ascidians, sponges, hydroids etc. cause severe economic losses because of the increased friction (and therefore increased consumption of fuel), or increased resistance to waves or currents (for static structures such as off-shore rigs), and because of decreased un-docking time.
In order to solve the fouling problem several antifouling paint technologies have been developed. Some technologies are based on the principle of incorporating biologically active agents into the paint. However, in order to obtain a satisfactory incorporation and a proper controlled release of the biologically active agents, the mechanical properties of the antifouling paint, e.g. the mechanical strength of the paint and the ability of the paint to adhere to other paints, may be impaired.
Another antifouling paint technology that has been investigated for a number of years, is the use of self-polishing antifouling paint compositions in which the polymer of the binder system is a trialkyltin derivative of a polymer containing carboxylic acid groups in the monomer segments, the alkyltin groups being situated on the carboxylic acid groups. However, the increasing problem of pollution with tin compounds in, e.g., harbours has led to intensive research efforts to provide tin-free self-polishing antifouling paints.
The search for binder systems for tin-free self-polishing antifouling paints, on the one hand having inherent self-polishing properties and exhibiting good capabilities for incorporation of biologically active agents, and on the other hand being able to convey a good mechanical strength of the paint film, has so far been a difficult task.
One way of obtaining binder systems for antifouling paints, such as for tin-free self-polishing antifouling paints, is to employ substances such as rosin or rosin equivalents as part of the binder system. Rosin or rosin equivalents has a number of highly desirable properties for use in antifouling paints; due to its water solubility it is capable of releasing biologically active agents into the water at a controlled rate. Also, it is compatible with a large number of binder components; this facilitates the formulation of a final coating product. Furthermore, it is readily available, relatively cheap and originates from a self-renewable natural source. In principle, the water solubility gives the opportunity of obtaining a high polishing rate in a rosin-containing paint if a high proportion of rosin or rosin equivalent is incorporated. However, inclusion of a high proportion of rosin or rosin equivalents in order to ensure a polishing rate optimal for practical purposes leads to an antifouling paint having severe mechanical deficiencies, such as cracking tendencies and poor resistance to weathering.
Therefore, due to the inherent mechanical deficiencies of such self-polishing binder systems, their polishing properties can not be fully expressed. The applicant's previous application, WO 96/15198, provides solutions to this problem, however, the applicant has now, after further development work, found important improvements and alternatives to the invention previously described.